期刊
CHEMELECTROCHEM
卷 8, 期 8, 页码 1464-1472出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/celc.202100084
关键词
anion redox; oxygen redox; layered oxides; cathodes; first-principles calculations
资金
- National Research Foundation of Korea (NRF) - Korean Government (MSIT) [NRF-2020R1I1A1A01072724, 2019R1F1A1052498, NRF-2020R1C1C1012308]
- Kyung Hee University [KHU-20201108]
- National Research Foundation of Korea [2019R1F1A1052498] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
This study investigates the mechanism of P2-type oxide in OR-induced two-phase reaction through experiments and first-principle calculations, revealing the crucial role of Li ions in activating OR reactions and controlling OR participation in the charge-compensation process.
Unlike cathodes for lithium-ion batteries, oxygen redox (OR) processes at a high voltage (approximate to 4.2 V) during the first charge in sodium-ion batteries (SIBs) employ some Li-incorporated Mn oxides that is recovered during subsequent discharge. To determine the intrinsic origin, P2-type Na-0.6[Li0.2Mn0.8]O-2 exhibiting a reversible OR-induced two-phase reaction was investigated using experiments and first-principle calculations. First, operando X-ray diffraction results in reversible P2-Z phase transformations and thermodynamic analysis show the two-phase reaction features Li migration into the tetrahedral sites from the transition-metal layer in the latter phase. Second, Li-induced decoupling of the oxygen 2p-electron led to selective anion redox activity depending on the oxygen sites that are Li-rich (redox-active) and Mn-rich (redox-inactive) environments. Third, redox-active oxygen coordinated to the Li vacancy predominantly participates in the formation of peroxo-like dimers with distortion of the MnO6 octahedron, as observed in the reversible extended X-ray absorption fine structure spectra during the OR reaction. Considering three physicochemical perspectives, we reveal that Li ions play a role in activating OR reactions and control OR participation in the charge-compensation process. Our findings suggest that the Li/Mn ratio is a critical factor for achieving a reversible OR reaction, and broaden the possibilities of exploiting OR to reach high-energy densities in next-generation SIBs.
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